1. Field of the Invention
The invention relates to a signal transmission method, more particularly to a signal transmission method that is suitable for use on a mobile device, a portable reader, a POS machine having a Java card-based design, or the like.
2. Description of the Related Art
FIG. 1 illustrates circuitry of a conventional mobile device 900. The mobile device 900 includes a baseband module 910, and an electronic card slot 920 that is coupled to the baseband module 910. The electronic card slot 920 is typically for receiving a subscriber identity module (SIM) card therein so as to electrically connect the SIM card and the baseband module 910 for communicating with the baseband module 910.
In order to accommodate a growing need for frequent use of commercial applications (e.g., online transaction) that require a high security level on the mobile device 900, another identification mechanism is needed (e.g., a bankcard, another SIM from a separate mobile telephony service provider, etc.). Conventionally, such identification mechanism is implemented in the operating system of the mobile device 900 using software. Nonetheless, the software-based identification mechanism may face safety threat from malicious programs (e.g., a Trojan horse), and as a result, a hardware-based identification mechanism is more preferable. However, the hardware-based identification mechanism is an external device (e.g., an electronic card) that must be physically connected to the mobile device 900, such that an additional expansion slot may be required. Since the electronic card slot 920 is only configured to communicate with the baseband module 910, and the identification mechanism may need to communicate with other modules in the mobile device 900, using the electronic card slot 920 to receive the hardware-based identification mechanism may be insufficient to fulfill such needs.
A number of solutions have been provided to address this problem. For example, a secure digital (SD) card slot 930 and/or a universal serial bus (USB) port 940 can be used to receive such hardware-based identification mechanism. But such solution may not be preferable due to the fact that the communication specification used by the hardware-based identification mechanism (i.e., International Organization for Standardization (ISO) 7816 specification) may not conform with that used by the SD card slot 930 and the USB port 940, and that some mobile devices 900 (e.g., iPhone) do not have the SD card slot 930 and the USB port 940.
Another solution involves implementing the hardware-based identification mechanism onto a thin film that can be attached to the SIM card. But the thickness of the thin film that adds to the attached SIM card renders the SIM card difficult to be received by the electronic card slot 920, sometimes even requiring a hole be drilled in the SIM card in order to fit in the electronic card slot 920.